1. Field of the Invention
The present invention relates to a method of manufacturing a chip-type ceramic electronic component that is suitable for surface mounting.
2. Description of the Related Art
Electrolytic plating of external electrodes of a chip-type ceramic electronic component has the problem of changing characteristics due to corrosion and dissolution of an exposed surface of a ceramic sintered compact. Therefore, in electrolytic plating, an insulating layer such as a glass layer is previously formed on the surface of the ceramic sintered compact, for preventing corrosion of the ceramic sintered compact.
FIG. 6 is a sectional view showing a conventional chip-type ceramic electronic component (chip-type thermistor). As shown in FIG. 6, a chip-type thermistor 11 includes a ceramic sintered compact 12, a glass diffused layer 13 located near the outer surface except at both ends of the ceramic sintered compact 12, and external electrodes 14 disposed at both ends of the ceramic sintered compact 12. Each of the external electrodes 14 includes an underlying electrode layer 14a formed by baking Ag, and a plated layer 14b formed on the underlying electrode layer 14a and including two layers of Ni and Sn (refer to, for example, Japanese Unexamined Patent Application Publication No. 2000-124007).
The ceramic sintered compact 12 is obtained by laminating a plurality of ceramic green sheets, and press-bonding the ceramic green sheets to form a ceramic laminated product, and then sintering the ceramic laminated product. Specifically, as shown in FIG. 7, a predetermined number of ceramic green sheets 16a each having glass paste 15 coated at both side ends of a main surface are laminated, and ceramic green sheets 16b each having the glass paste 15 coated over the entire main surface are placed at the top and bottom of the laminate of the ceramic green sheets 16a, and then the resultant laminate is press-bonded to form a ceramic laminated product.
In sintering the ceramic laminated product, the glass components contained in the glass paste 15 diffuse to the vicinity of the outer surface of the ceramic sintered compact 12, forming the glass diffused layer 13.
However, when the ceramic laminated product is sintered at a high temperature, the glass components of the glass paste are likely to excessively diffuse to the vicinity of the outer surface of the ceramic sintered compact. Therefore, as shown in FIG. 8, cavities 17 occur in the glass paste-coated portions in the ceramic sintered compact 12. As a result, in electrolytic plating of the external electrodes 14, a plating solution enters into the ceramic sintered compact 12 through the cavities 17 to cause the problem of corrosion of the ceramic sintered compact 12.